05-01-2010, 01:54 PM
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The cause is nutrient-related in most cases. I have seen charts elsewhere about symptoms and probable causes (i.e., which nutrients are missing or in excess to cause this and that), but I don't put faith in these as so many of the symptoms can be caused by different nutrient issues and it becomes a case of doing this and that hoping to hit the right one eventually. I don't like such an approach. Also, Tom Barr has told me that these "symptom" charts are quite unreliable because many are based on terrestrial plants, quite another thing.
Plants need a fairly specific balance of 17 nutrients; too much of this or that nutrient can sometimes cause plants to shut down assimilation of other nutrients, etc. Although some aquarists have success with substrate-only nutrients, many do not and find a liquid fertilizer necessary. First, what exact nutrients are in the enriched substrate? Flourite has 14 listed, so that's OK. [The missing three from their list are normally provided by fish and biological processes.] Now, I have no idea as to how much of each of these is in the Flourite and how quickly they are released. Seachem says it never has to be replaced. In my opinion, this is an impossible claim; the nutrients have to be exhausted at some point in time, but we can allow it will take a long time probably. You have it mixed with regular gravel you say, so that lessens the quantity of nutrients.
My initial general suggestion would be to use Seachem's Flourish Comprehensive Supplement once a week and monitor the plant's response over 2-3 weeks. But I would also like to know your water parameters (pH and hardness) and which specific swords (species) are being affected. Could you attach photos? I might have further suggestions if I see this for myself.